This invention generally relates to the art of electrical connectors and circuit cards. Particularly, the invention relates to a system and method for decreasing the impedance through a connector to board interface by increasing the capacitance thereof.
In today""s high speed electronic equipment, it is desirable that all components of an interconnection path be optimized for signal transmission characteristics, otherwise the integrity of the system will be impaired or degraded. Such characteristics include risetime degradation or system bandwidth, crosstalk, impedance control and propagation delay. Ideally, an electrical connector would have little or no affect on the interconnection system regarding these characteristics. An ideal connector would be xe2x80x9ctransparentxe2x80x9d. In other words, the system would function as if circuitry ran through the interconnection and there would be no effect on the system whatsoever. However, such an ideal connector is impractical or impossible, and continuous efforts are made to develop electrical connectors which have as little effect on the system as possible.
Impedance and inductance control are concerns in designing an ideal connector. This is particularly true in electrical connectors for high speed electronic equipment, i.e., involving high frequencies. As example of such connectors is the popular type of electrical connector commonly called an xe2x80x9cedge cardxe2x80x9d connector. An edge card connector is provided for receiving a printed circuit board or edge card having a mating edge and a plurality of contact pads adjacent the edge. Such edge connectors have an elongated housing defining an elongated receptacle or slot for receiving the mating edge of the printed circuit board. A plurality of terminals are spaced along one or both sides of the slot for engaging the contact pads adjacent the mating edge of the board. In many applications, such edge connectors are mounted on a second printed circuit board. The mating xe2x80x9cedgexe2x80x9d board commonly is called the xe2x80x9cdaughterboardxe2x80x9d, and the board to which the connector is mounted is called the xe2x80x9cmotherboardxe2x80x9d.
Another example of such connectors are board to board connectors in which a plug connector mounted on a first board has an insertion portion with terminals thereon for insertion into a receptacle connector mounted on a second board with terminals in a recess for receiving the insertion portion of the plug connector. The terminals in the plug connector mate with terminals in the receptacle connector to connect conductors on respective boards.
A problem with these connector systems as described above is that there often is an impedance mismatch between the connected boards. This impedance variance is caused by the connector having a relatively high impedance. One solution for controlling this impedance mismatch is to vary the structure of the connector, itself, and particularly the terminals of the connector. However, such changes are relatively expensive and involved. The present invention is directed to a system and a method for controlling the impedance through a connector in a very simple and inexpensive manner, by changing the configuration of the contact pads or conductors of the board itself. In essence, the capacitance of the board can be increased to decrease the impedance through the system.
An object, therefore, of the invention is to provide a new and improved system and method for controlling the impedance of a connector by varying the capacitance of the board itself.
According to one aspect of the invention, a connector system includes a connector and a circuit board. The connector includes a housing having an electronic component mating portion. A plurality of signal terminals and ground terminals are mounted on the housing along the electronic component mating portion. The terminals have contact sections extending to the mating portion. The circuit board has a first surface and a ground plane at least near said first surface and a plurality of signal conductors and a plurality of ground conductors on said first surface for engaging the contact sections of the signal terminals and the ground terminals, respectively. The signal conductors have a greater area than the ground conductors to increase the capacitance of an interface between the signal terminals and the signal conductors.
In another embodiment, a connector system includes a connector having an elongated housing with an elongated card-receiving slot. A plurality of signal terminals and ground terminals are mounted on the housing along the slot and have contact sections extending into the slot. In the preferred embodiment, the signal terminals alternate with the ground terminals along the slot. A circuit card has an edge insertable into the slot, a ground plane at least near the edge and a plurality of signal contact pads alternating with a plurality of ground contact pads along the edge for engaging the contact sections of the signal terminals and the ground terminals, respectively. The size of the signal contact pads are varied relative to the ground contact pads to vary the capacitance in the area of the terminal-to-board interface. For instance, by making the signal contact pads with greater area than the ground contact pads, the capacitance of the circuit card is increased which, in turn, decreases the impedance through the system.
In the exemplary embodiment, the signal contact pads are wider than the ground contact pads in a direction longitudinally of the edge of the circuit card. The centerline-to-centerline spacing between the signal contact pads and ground contact pads is equidistant along the edge of the card. The ground plane is embedded in the card. A plurality of the signal and ground terminals are mounted on the housing along both sides of the slot, and the circuit card has a plurality of the signal and ground contact pads on opposite sides of the card near the edge thereof.
According to another aspect of the invention, a method of manufacturing a connector system as described above, including the connector, the signal terminals and ground terminals, the circuit card and the signal and ground contact pads along the edge of the card. The method includes the steps of determining a desired impedance through the system, and selecting a given size of the signal contacts pads relative to the ground contact pads which effect a given capacitance resulting in the desired impedance.
Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings.